1. Field of the Invention
This invention relates to chemical heat pump system utilizing reversible decomposition-addition reaction. More particularly this invention relates to chemical heat pump system of improved efficiency.
2. Prior Art of the Invention
Recently, heat pump were watched with keen interest since they are useful to save energy because they can recover much energy from lower heat sources using small amounts of energy. In this case both mechanical energy and chemical energy can be used as said small amount of energy.
In a case of so called compression type heat pump using mechanical energy, not only is the so called coefficient of performance (C.O.P.) limited but also temperatures of lower heat source and temperatures of higher heat source (from which energy is recovered) are limited since there are limitations on safety or heat stability of the heating medium and on mechanical strength of the system.
On the other hand, in a chemical heat pump utilizing reversible endothermic and exothermic reactions, the temperature ranges of the lower heat source and the higher heat source in the chemical heat pump system can be broadened, by selecting the raction system.
For example, when a reversible reaction, (e.g. a secondary alcohol decomposing to a ketone and a hydrogen) is utilized, the temperature of the lower heat source is about 55.degree. C.-80.degree. C. and that of the higher heat source is about 160.degree. C.-230.degree. C. (e.g. "Arts for Heat Accumulation and Heat Increase" 117 pages, (1985), Chemical Engineering Symposium Series 8, Edited by Chemical Engineering Association). On the other hand when a reversible reaction between a benzene and a cyclohexane--dehydrogenation and addition of the hydrogen--is utilized, the temperature of the lower heat source can be more than 200.degree. C. and the temperature of the higher heat source may to be from about 300.degree. C. to about 400.degree. C. (ibid., pg. 123).
Generally, a dehydrogenation reaction is an endothermic reaction and a hydrogenation reaction is an exothermic reaction. Therefore, by carring out these reactions in separate reaction vessels, each vessel becomes an exothermic reaction vessel or an endothermic reaction vessel. Namely, by circulating a reactant between the exothermic reaction vessel and endothermic reaction vessel, energy can be recovered through a heat exchanger provided between said exothermic reaction vessel and endothermic reaction vessel. Using this principle alone, however, the efficiency as heat pump system is insufficient. This is because the hydrogenation reaction is negligible when the temperature of the reaction vessel is to high--this fact is consistent with Le Chatelier's principle. Therefore, it is necessary to shift the equiribium by carring out the hydrogenation reaction under compression.
As a new method to solve the above mentioned problem, we have already disclosed a chemical heat pump system utilizing a mixed solution for the reaction system of the hydrogenation--dehydrogenation reversible reaction, in which a hydrogen absorbing alloy was dispersed to make slurry (Japanese Patent Application No. 47350/'85. This system is called "the conventional system" in this specification). However, this system has points to be improved since (1) the hydrogen absorbing alloy is very expensive, (2) a passage of the alloy through the system causes damage because the abrasive slurry is always circulated in the system and shortens the lifetime of the system, (3) the hydrogen absorbing alloy becomes to catalyst to lower the temperature of the higher heat source by lowering the reaction temperature of the exothermic reaction.
We completed this invention as a result of our earlier work concerning a system using no hydrogen absorbing alloy to solve the above mentioned defects. We found that the C.O.P. of the whole system can not be improved if the whole system is only compressed (this system is called vapor compression type in this specification) to carry out the exothermic reaction under a compressed condition. However, the C.O.P. of the whole system can become large if the liquid phase and the gas phase are separated from each other and then each phase is individually compressed.